041 and 455 pontiac vacuum

[BLUE TA]

hi guys, Im building a 455 and just bought a 041 cam. I know cliff has had great results with this combo. my question is will I have enough vacuum for my power brakes. 6x8 heads, cliff designed q jet, 68 oem intake and th 400 2500 stall. ra exhaust manifolds. 74 TA. will I need rhoads, more compression? thanks, mike

[Cliff Ruggles]

Are you going to zero deck the block and use a thin head gasket?

The 6X-8 heads are 101cc so the compression ratio will be pretty low.  I'd do what you can to get it as high as possible/practical if you want to run the RAIV cam in it.

I like to see at least 9.5 to 1 compression, 10 to 1 or a tad more is optimum for that cam in a 455 build with iron heads.

I did ONE 455 here with 6X-8 heads on it and it required Rhoads lifters to be happy and actually worked out well.  Just a tad "soft" at low RPM's but from 3000 rpms and up it was an ANIMAL!.......

[BLUE TA]

thanks  cliff, yes I will increase compression to at least 9.5 to 1. will it stil have enough vacuum for the brakes. will I need rhoads for sure?

[Cliff Ruggles]

Yes, it will work best with Rhoads lifters and 9.5 to 1 is a good move as well......

[old cars]

Something like a Crower 60918 would have been a better choice. And no rhoads lifters required to crutch it. That 041 cam will have no balls on the street unless you have around 411 gears.You can to better

[BLUE TA]

thanks guys for the info BLUE TA

[Cliff Ruggles]

Back in 2004 I had my 455 with 6X heads on the dyno with a Crower 60919 cam.  It was topped with Rhoads lifters and high ratio (1.73) rocker arms.  The engine cranked out 455.4hp and 540tq.  The dyno session was part of the KRE aluminum cylinder head testing and Popular Hot Rodding Engine Masters articles that followed.

A few years later I decided to "upgrade" the cam we hired Comp to grind a larger 240/248/112 cam with .060" more lift than the "041" cam.

On the dyno the bigger cam was down 10hp/22ft lbs torque over the 041.  Hum?  I moved the cam around and tried timing/fuel and it just got worse.

I pulled the custom ground Comp cam and installed a custom ground hydraulic roller cam with 284/296, 230/242 @ .050" 112LSA.  It had .361" XFI lobes so a pretty "hefty" camshaft compared to the puny flat 041 cam.

To my surprise the engine only picked up 3hp/4ft lbs torque with the HR cam?  Not nearly what I had hoped for considering the $1200 investment.  It did idle just a tad better, about 13.5" vacuum instead of 12", but no huge gains in power like I was expecting. 

Something to be said for using a long seat timing cam with high ratio rockers and Rhoads lifters, sure surprised me at that time........Cliff

[old cars]

And dyno numbers peak hp/torque don't represent how a car will drive/perform on the street. I said Crower 60918

[Too Fast]

OP, I use an 041 in my LeMans.  It has about 9-10" vacuum at 850 warm idle.  Is that enough for consistent power brakes?  IMO, no.  I know what to expect, and I have to stand on the brake pedal sometimes to stop, but it still isn't as bad as a car with no power brakes.  My car is an .030 over 400, I think your 455 will have slightly better idle vacuum.

You could also use a vacuum cannister with a check valve in line with the line going to your power booster.  Ford did that on a lot of cars in the late 70s.  Those cans looked like Hi C juice cans.  IIRC they were half gallon sized.  Brings back memories of what my mother bought lol.